Sediment as a Refuge Spot for Planktonic Crustaceans

The littoral zone of shallow water bodies (SWB) is often considered in relation to predator-prey interactions. In this study we assumed that the littoral sediment serves as a refuge for planktonic microcrustaceans, mediated by size-dependent fish predation. In order to recognise the impact of fish on their prey, we determined: (i) the assemblage and size structure of crustaceans and fish; and (ii) the biotic interactions along the gradient of the heterogeneity of the littoral zone. The results showed that in the sediment of macrophyte-dominated SWB, large-sized cladocerans predominated and were preyed upon by smaller-sized fish. In the sediment of macrophyte-absent SWB, large-sized copepods dominated, due to the predation risk of larger-sized fish. Cladoceran females with egg broods mostly selected sediment as shelter. Cladocera/Copepoda ratios were lower in the littoral of vegetated SWB, and higher in unvegetated SWB. The ratios in the adjacent sediment revealed an opposite pattern. It is important to point out the findings of planktonic crustacean species in the sediment of SWB are not recorded in the littoral water. The result of this study will contribute to the knowledge of defence strategy mechanisms developed by zooplankters against predators.